Posted
by
Roblimoon Tuesday May 21, 2013 @02:22PM
from the it's-all-about-the-air-cushion dept.

What little boy or girl never wanted a hovercraft? Something loud that could travel over water, pavement, maybe even over a plowed field or through a swamp? Ben King obviously wanted one, so after he grew up and got his PhD in physics and found a good job, he founded Lone Star Hovercraft. Timothy Lord interviewed Ben at the Austin Mini Maker Faire, and we also found some video of Ben flying (is that the right word?) one of his hovercraft on a lake that we spliced into the interview to liven it up a little. Vroom!

Ben:
My name is Ben King. I’ve got a small company called Lone Star
Hovercraft, and this is one of our prototypes we’ve been
recently developing. It is built using what you will probably call
pretty conventional construction techniques. It is just a thin layer
of fiberglass on a foam core. So it is very light weight and very
strong. The hovercraft itself the whole weighs about 150 lbs. And
the engine about doubles that; it is about 300 lbs., ready to fly.
So it is very strong, but very light weight. We are working on a few
projects. We do some that are conventionally built; we are also
working on some projects that are designed to be more like a quick
build kit. Because these take anywhere from six months to even a
couple of years to build. There are people who want to be on the
water, and want to fly but don’t have quite that much time to
build from scratch. So we are looking at both conventional
hovercraft and also more of a kit type hovercraft just like quick
assembly.

Tim:
Now if this will take so many months to build, how long can it take
to learn those techniques? This is your first one, is it your fifth
one?

Ben:
This is the third full-size hovercraft I built. I started with plans
from a couple of companies, and they really spell out all the
processes you use, all the materials so it is a good way to
learn – building from plans. And I started even before that
doing radio controlled hovercrafts, so everything from electric
motors using radio controlled airplane parts up to engines on the
leaf blowers and weed whackers and things like that.

Tim:
How about that? You’ve got an engine back here. What kind of
an engine is this?

Ben:
This is a Generac brand engine it is 40 hp. It is a 1 liter V twin
off of a basically it is the largest consumer grade
generator you can get. And you could also source these engines
relatively cheaply and they are very quiet, very reliable. And it is
a really good power plant for a hovercraft this size.

Tim:
Now you mentioned the idea of making kits. And you’ve got a
model over here. Can you talk about modeling?

Ben:
Sure, so this is a ½ scale mockup of a kit that I am working
on. It is made entirely from a CNC router cut plywood. And the idea
is it goes together much like a IKEA furniture, so it all slots and
grooves. And there is really minimal measuring, minimal cutting - you
basically will get the kit and put it together and hopefully,
customize it to make it your own, with your own power plant, your own
paint things like that. But the idea is to take a lot of the
grueling work out of the process, and get you the fun part faster.

Tim:
So what would people need to add if they bought a kit to make a
hovercraft like this? What parts would you include and what parts
would someone else need to buy?

Ben:
We would try to include most of everything you would need for the
full kit. So basically the whole kit, and then probably also the
engine is an option, and then a reduction drive that slows the
propeller down, propeller and then also the molded ducts so that is
the duct in the back there, that will be part of the more or less
standard kit. And for customization, you could add whatever kinds of
controls you like, whatever kinds of paint jobs you like, things like
that.

Tim:
Now this boat, how maneuverable is it, compared to a canoe or a row
boat?

Ben:
It is very maneuverable once you have the knack for it, it takes a
little bit of practice, but it is often compared to flying a bar of
soap. So you have to look as far ahead as you can when on the water,
or wherever you are and look for obstacles coming up, and you have to
turn in advance, so it flies like a spaceship or an airboat, you turn
and you push in the direction you want to go. And so you don’t
have the steering that you are used to in a car or like the brakes
where you have instant feedback. You really got to anticipate where
you want to go and fly ahead about 10 seconds.

Tim:
For propulsion, you have only got the thrust in one direction?

Ben:
Right, right.

Tim:
How much that of that motor’s 40 hp goes into actually lifting
the craft?

Ben:
About a third is the general rule of thumb. So about a third is
directed beneath the craft and the lift air box that you see in the
back. Part of that actually inflates this vinyl skirt, about 10
percent of the air, that’s actually sealed, so the remaining 90
percent goes beneath into the center of the craft, into what’s
called the plenum that actually lifts it.

Tim:
Is the skirt your own design as well? It is the whole thing?

Ben:
It is pretty standard. It is called a bag skirt. So these are
pretty standard designs.

Tim:
And you described this as a homemade project? Is it literally built
in your garage?

Ben:
Built in the garage, yep. This is the third one. I’ve got a
decent garage now, so I build there. The first one I built in a
living room of a third floor apartment, and lowered it out the
balcony window.

Tim:
You must have a pretty big staff?

Ben:
I had some buddies help me out. Yeah. So it is home built so it is
built in the garage, and you really can make some pretty cool stuff
just in the garage with everyday things you have around the house.

Tim:
Now where are you going to actually drive your hovercraft?

Ben:
Usually it is licensed as a boat, as you can see, it has got
boat tags for the state of Texas. You can ride them pretty much on
any reasonably flat surface, so grass, ice, mud. There aren’t a
lot of public places you can ride, like on grass, or land. So
generally they pick a lot of water. That is the most readily
available place to go. So lakes and rivers.

Tim:
Was licensing a hard thing to get done?

Ben:
Not at all. In Texas, it is really very easy. You license it as a
homemade vessel, you basically tell them how much power it has, how
much it weighs, and that’s pretty much it.

Tim:
And you are here at the Maker Faire, why so?

Ben:
Well, I like the general atmosphere, it is really exciting, and also
we’ve been doing this for a long time, using really
conventional methods, and what I find is it is really exciting to see
all the new tools that are becoming available, even just in the last
two or three years. So we are already using a CNC router, we use
water jet cutting, we are starting to get into 3D printing, so there
is a lot of really cool technology here that can be used directly in
making hovercraft and vehicles like this. So it is really cool to see
what’s cutting edge and what people are doing.

Tim:
I know you can’t pin down a price on a product that is not out
for a while, but in general, what sort of price comparisons might
somebody find in looking at a new hovercraft versus what you hope to
do in making the kit?

Ben:
We are hoping if you look around for production turnkey
hovercraft they start at around $20,000 or a little bit less –
it is pretty high for a weekend vehicle. We are hoping to come out
with a kit that might be like a third to less than half maybe of that
price. But with a little bit of labor, you can have a similar craft
that is high performing at a pretty small fraction of the price.

Tim:
Speaking of weekend, this isn’t your day job, is it?

Ben:
No it is not. It is a side a small business along the side.

Tim:
What’s your background and what do you do during daytime you
work week?

Ben:
So my background is in physics, I got my PhD in physics; I studied
fluid dynamics so a lot of it really relates well working on
props and engines is really exciting. So I work at an energy company
during the day doing research.

Tim:
Anything else people should know, if they want to find out more about
this?

Ben:
I am sorry

Tim:
What would people need to know if they want to find out more about
this?

Ben:
Those who want to find out more, we try and keep our website pretty
up to date, so it is www.lonestarhovercraft.com.
So we’ve got several build logs that have complete
start-to-finish construction pictures, we have a lot of work on
engines, videos, things like that. So we try to make it a really
useful resource for builders and people wanting to do their own
craft. So that is the best source.

When I was a teenager, the father of a wealthy school friend won a hovercraft in a card game. It looked quite similar to the one above. It was powered by a Bombardier snow mobile engine and was extremely loud. It would only hover when the fan was running, as the airstream for the hovering air came from a diverted stream of about 1/3rd of the prop wash air. Steering it felt a lot like trying to push one of those Ikea shopping carts that has four pivoting wheels...during a turn, you end up going sideways for a time. Going over water, it felt not unlike being on a loud boat or a seadoo. Going over land, it felt like being on a loud ground vehicle. The cool part came when we could drive it over a mud flat which alternated between sand and water. It really was an unusual sensation. The problem was that it ate fuel like crazy. It was far worse than a regular boat. The other problem was that when it came to a rest, the sand started to grind down the bottom. We did mitigate this by adding some fiberglass enforced wooden rails. Overall, it was great fun as a teenager, but even if I had the money to dump on such a toy, I doubt I would.

I miss the hovercrafts that used to cross the English Channel. Very cool machines that would make you throw up in anything but the calmest seas - http://www.youtube.com/watch?v=A02u03xhpPw [youtube.com] . Victims of the EuroStar and other circumstances. You want fast, you go by train, you want low-cost, you go by ferry.

I crossed on one when I was little. Maybe nine or ten. Fairly choppy weather. I remember I was reading a disney comic of some sort. One of the stories definitely involved Mickey Mouse holding some people at gunpoint with a machine gun, but it turned out the guns had no firing pins. Odd the things you remember. Anyway, I didn't get sick at all. It's sort of odd that. I used to get carsick when I was younger, but then I suddenly reached a point where I never seemed to get any sort of motion sickness at all an

You're full of speculation. And you ignore the fact that sound travels beyond property lines. Basically, you don't seem to care how your actions affect others. And you encourage suicide. I'd say you're the one who needs to stop talking.

When I was at school about twenty years ago some of the kids built a similar-sized hovercraft as a project and used to ride it around the playground. Given how cheap our school was, it can't have cost them much other than a second-hand engine and some wood for the body and fins and rubber for the skirt.

Recently I read an old Arthur C Clarke article from the 50s or 60s about how hovercraft were to be the future of transport and no-one would want wheels any more. I guess it just wasn't this particular future.

Recently I read an old Arthur C Clarke article from the 50s or 60s about how hovercraft were to be the future of transport and no-one would want wheels any more. I guess it just wasn't this particular future.

I always wanted a hovercraft in the future, but I was too lazy to learn Esperanto.

Their problem is (1) active suspension, and (2) lack of directional stability.

(1) If your car is stopped at a red light and its hybrid engine shuts off, you're burning no energy. A hovercraft stopped at a red light is still burning energy to maintain the air cushion. Same thing is true at speed - the car's suspension keeps the chassis off the ground at (close to) zero energy cost. A hovercraft is always burning energy to stay off the ground.

(2) When you drive a car on a road, the wheels are physically locked (up to the coefficient of static friction) with the road. You have to exert a significant amount of torque to the car before the wheels unlock from the road and the car starts to spin/skid. So a car is pointed in the direction it's traveling nearly all the time. This reduces directional control to a simple one degree of freedom problem - the more you turn the steering wheel, the faster you change direction.

With a hovercraft, the slightest torque on it will change its orientation. Even an airplane does better - its high forward velocity generates a stabilizing aerodynamic force on the tail to keep it pointed somewhat in the direction of travel. OTOH, a hovercraft's slower forward velocity means it needs to rely on vectored thrust for orientation stability. So now you've got a direction of desired travel which is mostly uncoupled from the direction the hovercraft is pointing (yaw). And if you do get turned away from the direction you're traveling, a righting moment to yaw it in the right direction again will also impart a small translation, thus changing your direction of travel slightly.

It's actually more akin to piloting a spacecraft in 2D than it is driving a car. You can do tricks like spinning 360 degrees without changing your direction of travel (much). Which is fun in theory, and perhaps useful if you're in combat. But it's added complexity which makes piloting one more dangerous that driving a car for the average layperson.

Also, the advantage that it can travel over water is a bit of a misnomer. At low velocities, a hovercraft on water acts pretty much the same as a displacement hull. The air cushion sinks down until it's displacing the hovercraft's weight in water. Moving forward then involves pushing the hovercraft uphill over the front lip of the depression in the water it creates, just like a displacement hull. You're only slightly better off than if you were in an amphibious car. As you pick up speed, the wave resistance begins to decrease. The tradeoff point where it becomes more efficient than a planing hull varies with size, but it's typically around 30-50 knots, which is why they haven't displaced planing boats as the recreational watercraft of choice - there's little to no advantage at these speeds. For it to be nearly as efficient as traveling on a solid surface, you have to be moving at close to 100 knots over the water.

One time I was being chased by this maniac in a hovercraft. He even ran me over on the beach. I got some sand in my mouth, but I was unharmed. He chased me all through town. Eventually I grabbed a sword from an antiques shop and commandeered a Lamborghini. Playing chicken with the hovercraft, I swerved at the last moment and was able to slice up its tender bits. So hovercrafts are quite vulnerable to swords. I still was pretty lucky though.

good reason they aren't more popular in the one to four person size range, they get horrible fuel economy. My two friends get 4 to 6 miles per gallon on water with theirs. funny the claims the vendors make of them using half the fuel of a boat, the hovercraft is carrying only people but a boat will be able to have cargo too.

Plans for these have been around forever. Many, many people have built them.hovercraft.com [hovercraft.com] has many plans and kits for sale.

When my son was 9, he called me at work one day. "Dad, do we have a leaf blower?"....Yes..."Do we have a piece of plywood 4 feet wide?"....Yes. (I can see the wheels turning)...He goes on to list a bunch of other parts.'Ok, dude....why?'"I have a science project! I want to make a hovercraft!"

"OK then." He had gone online and found plans for a simple floating platform. No forward thrust, powered by a leaf blower.

It worked well enough to float my fatass down the driveway.

He got an A. My wife freaked out when I chose this as a teaching moment in how to use a circular saw.

... did the first hovercraft crossing of the Cook Strait in a home-built hovercraft. He then checked out the ferry times for the return trip home, checked his watch, and shortly after did the second hovercraft crossing of the Cook Strait in a home-built hovercraft.

Homemade hovercraft used to be a big thing since at least the '50s or '60s (and for all I know still are). Typically made by putting a prop on a vertical-axle lawnmower engine and building a simple vehicle body with a fan shroud in the middle.

There was a classic disaster that happened to a LOT of people who did this:

After they'd played around on land with it for a while they'd decide to test how it would perform on water. So they'd take it down to the local park-on-a-lake, fire it up, and drive out onto t

Perform this search experiment with Hoverbike/Concept Hoverbike as your search term and the disparity is worse - the real world things, even the expensive ones always look like they've been made in some back yard.